Nothing. Bringing a bunch of special agents along with you to a meeting is intimidating, though.

I suppose in their defense, they may be the particular agents working on the San Bernadino case, who arrived to explain exactly why they need the access or whatever.

The way powerful people often maintain control of a situation is through contrivances such as unusual dress, unusual ways of speaking, unusual rituals or by having a large entourage.

If you analyse each element closely it's clear that they're silly. Why do they need earpieces in when visiting Apple? Why must all the cars match? Why must they dress in the same way? Why do they need to bring all those people, what are they all doing?

But the point is, when faced with something new and strange, people often pause and withdraw. This allows you to dominate the situation and prevent dissent.

Earpieces are probably worn routinely, just as many other people you may see walking around.

Large organizations typically procure fleets of vehicles that are all the same model. This reduces development and maintenance costs.

Many institutions, particularly law enforcement, have strict dress regulations and many distribute their own uniforms appropriate to the particular position.

Yes, and those things are done for the exact reasons the parent comment mentioned. Even comedies like Brooklyn Nine Nine recognize this fact (one episode had a bit about a detective refusing to wear a tie). They wouldn't bother with uniforms if they had no effect.

Its intimidating for the same reason that having the kgb show up for a russian companies meeting would be intimidating.

Special agents who wear earpieces are people who have been trained to respond swiftly and decisively when violence is called for. That's what the earpiece is for, to coordinate tactical action if necessary. Having a swarm of them show up at your place of business is obviously intimidating even if they're not actually planning or expecting violence.

You would expect the higher level officers and directors to be in plain clothes, normally.